Universal Functional Activity

When it is necessary to estimate activity coefficients where no data or very limited data are available, estimates may be made by using a group contribution method. In this case, a molecule is divided into fimctional groups, or subgroups of the molecule. These subgroups are assumed to act independently of the molecule in which they appear. Molecular interactions are accounted for by properly weighted sums of group interactions. Fredenslund, Jones, and Prausnitz developed the method for UNIQUAC and named it as universal functional activity coefficient (UNIFAC). Smith, van Ness, and Abbott report the equations for the activity coefficients of multicomponent solutions and their parameters. These equations are very... 

The UNIFAC (universal functional activity coefficient) method [16] is similar to the ASOG method and is based on the four postulates of Wilson and Deal [13] regarding solution of groups. In UNIFAC, the activity coefficient is made of two parts. 

The choice of a plasticizer is mainly ruled hy its compatibility with the polymer material involved. Indeed, as explained by the plasticization theories, plasticizer molecules have to deeply penetrate into the macromolecules network and remain stable inside. Thereby, the initial emulsion during the mixing process using an extruder or roll mixers requires a thermodynamically favourable plasticizer/polymer pair. In order to quantify the compatibility, several approaches have been developed. The most complex ones are the QSAR (Quantitative Structure-Activity Relationship) or UNIFAP (Universal Functional Activity coefficient for Polymers),which are highly effective, but need extensive amounts of data and consequently might be uncomfortable to employ in a first approach. 

Modeling of a semibatch reactor (Figure 16.1) enables to determine the reaction rate pseudoconstants. For lack of physical data, a number of assumptions have to be made. The volume of the liquid phase is the function of composition, temperature, pressure, and mass of EO reacted with raw material. At a constant temperature (185 5°C), the volume of the liquid phase increases due to an increased solubility of EO. However, the rate of change is relatively low compared to the reaction rate. The universal functional activity coefficient (UNIFAC) method [43] was used to calculate the activity coefficients. The method was adopted for the heterogeneous liquid-liquid-vapor system as the limited solubility of liquid components was observed. The... 

One possible approach is UNIFAC (universal functional activity coefficient) and its many variants, particularly UNI-FAP (UNIFAC for polymers) [1]. This is a classic group contribution methodology that relies on fitting of large data sets of various properties. In areas where these large data sets exist, the methods are most fruitful. But despite the enthusiasm of the proponents of these methods, there is not a reliable body of results applicable to the sorts of questions of interest to this chapter. 

The Wong-Sandler mixing rules extend the use of cubic equations of state to mixtures that were previously only correlated with activity-coefficient models. For many mixtures, the Gibbs-function model parameters in the equation of state could be taken to be independent of temperature, thereby allowing extrapolation of phase behaviour over wide ranges of temperature and pressure. For example, for (ethanol-h water) the activity-coefficient model reported in DECHEMA is at a pressure of 0.4 MPa and this model provides reasonable predictions of the phase boundaries at pressures up to 20 MPa. This means the method can be used with UNIversal Functional Activity Coefficient (known by the acronym UNIFAQ and other group-contribution methods to predict properties at elevated pressure. 

More reliable phase behaviour predictions for binary ionic liquid systems with carbon dioxide or organics come from group-contribution equations of state, such as the universal functional activity coefficient (UNIFAC) method, the group-contribution nonrandom lattice ffuid equation of... 

The UNIQUAC equation uses empirical data to obtain the molecular parameters in Table 7.4, but it has been modified to the UNIFAC (Universal functional activity... 

The lac repressor monomer, a chain of 360 amino acids, associates into a functionally active homotetramer. It is the classic member of a large family of bacterial repressors with homologous amino acid sequences. PurR, which functions as the master regulator of purine biosynthesis, is another member of this family. In contrast to the lac repressor, the functional state of PurR is a dimer. The crystal structures of these two members of the Lac I family, in their complexes with DNA fragments, are known. The structure of the tetrameric lac repressor-DNA complex was determined by the group of Mitchell Lewis, University of Pennsylvania, Philadelphia, and the dimeric PurR-DNA complex by the group of Richard Brennan, Oregon Health Sciences University, Portland. 

The end of 1970s was marked by extensive studies on the role of antioxidants in the normal metabolism of cell. There was drawn the conclusion that AO are universal modifiers of composition, structure, and functional activity of membranes and that many of their effects on cell metabolism may be interpreted from these posotions [44, 45]. There was discovered the physicochemical system of regulation of cell metabolism by membranes based on interrelation between membranes lipid peroxidation (LPO), on the one hand, and changes in the composition of membrane lipids and their oxidizability, on the other hand [46, 47]. 

PROSSER, 1., ALTUG, I. G., PHILLIPS, A. L., KONIG, W. A., BOUWMEESTER, H. J., BEALE, M. H., Enantiospecific (+)- and (-)-germacrene D synthases, cloned from goldenrod, reveal a functionally active variant of the universal isoprenoid-biosynthesis aspartate-rich motif. Arch. Biochem. Biophys., 2004, 432, 136-144. 

Eqs. (6.43) and (6.44) show that c/, and j/J are universal functions of f, which are controlled by a single parameter A. These functions are depicted in Figure 6.10. Physically, lower A corresponds to faster oxygen consumption along f. Note, that the ratio j/ch = f J does not depend on f. Furthermore, the activation and transport losses in (6.32) are constant along f. This is seen if we rewrite Eq. (6.32) as... 

It seems worthwhile to comment upon the quasi-steady state distribution function f(r, t) in this Ostwald ripening process. The mathematical verification of the fact that this distribution function/(r, t) can be written as a product/i(0 fii lr) (and f2(rlf) is a universal function even in cases where the initial distribution / (r, 0) is of Gaussian shape and of moderate width) is rather cumbersome and must be studied from the original work [33]. However, one may conceive the shape of the quasi-steady state distribution (which has a maximum between 0 r/F < 3/2 at r/F = 1.135 and is essentially zero at r/F > 3/2) by realizing that it is the interplay between the activity difference of the average activity of A in the solution matrix... 

A wide-spread and widely applicable procedure for the calculation of the activity or the activity coefficient of non-electrolytic liquid mixtures is the so-called UNIFAC (Universal Functional Group Activity Coefficient) method (Reid et al. 1977). T. Oihsi and J. M. Prausnitz reported about an extension of the procedure which can be used to determine the activity of substances dissolved in amorphous polymers (Oishi and Prausnitz... 

UNiFAC UNIversal Functional group Activity Coefficient)... 

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